Fundamentals of Concrete Concrete 101 - PowerPoint PPT Presentation

Loading...

PPT – Fundamentals of Concrete Concrete 101 PowerPoint presentation | free to view - id: 96f91-M2IxZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Fundamentals of Concrete Concrete 101

Description:

increased resistance to weathering. reduced shrinkage cracking tendencies ... Transport, place, consolidate, and finish with least delay ... – PowerPoint PPT presentation

Number of Views:3161
Avg rating:3.0/5.0
Slides: 34
Provided by: Jdie
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Fundamentals of Concrete Concrete 101


1
Fundamentals of ConcreteConcrete 101
  • Joseph E. Diedrich
  • Technical Service Manager
  • Southdown, Inc.

2
Concrete 101
  • Concrete is basically a mixture of two
    components
  • Paste
  • Aggregates
  • Paste (Portland cement, water, and air)
  • Aggregates (sand, gravel, crushed stone)

3
Concrete 101
  • Portland cement meets AASHTO M-85 or ASTM C-150
  • Type I, II, III, IV, V
  • Blended Portland Cement meets AASHTO M-240 or
    ASTM C-595
  • Type I(pm), I (sm), I (p), etc...

4
Concrete 101
  • Aggregate are divided into two groups
  • Fine - AASHTO M-6 or ASTM C-33
  • Coarse - AASHTO M-80 or ASTM C-33
  • Fine aggregate consist of natural or manufactured
    sand with particle size up to 3/8 inch
  • Coarse aggregate particles are retained on the 4
    sieve and range up to 6 inches

5
Concrete 101
  • Cement Water Air Fine Aggregate
    Coarse Aggregate

Cement paste constitutes about 20 to 40 volume
of concrete
6
Concrete 101
  • Cement is usually between 7 and 15 based on
    absolute volume
  • Water is between 14 and 21 based on absolute
    volume
  • Air volume ranges up to 8 based on top size of
    coarse aggregate
  • Aggregates, fine coarse complete the mix

7
Air Entrained Concrete
  • Why the difference between line 1 and line 2?
  • Line 1, small size CA, increased H2O and cement
  • Line 2, larger CA, less H20, air, cement

8
Non-Air Entrained Concrete
Cement Water Air Fine Aggregate Coarse
Aggregate
  • Similar to Air Entrained Concrete slide
  • See how aggregate size impacts water demand and
    amount of paste in the mix

9
Concrete Ingredients
  • Quality of concrete depends on quality of paste
    and quality of aggregates
  • each particle of aggregate is completely coated
    with paste
  • All spaces between aggregate is filled with paste

10
Quality of Concrete
  • Is determined by
  • W/C Ratio - Advantage of reducing water
  • Increased compressive and flexural strength
  • lower permeability
  • increased resistance to weathering
  • reduced shrinkage cracking tendencies
  • The less water used, the better quality of
    concrete, provided it can be consolidated
    properly.

11
Admixtures
  • Plastic and hardened properties of concrete may
    be
  • changed by adding admixtures
  • Admixtures are commonly used to
  • increase set time
  • decrease set time
  • increase workability
  • adjust other concrete properties
  • reduce water demand
  • entrain air
  • inhibit corrosion

12
Curing
  • Critical to durable concrete
  • Increases strength
  • Decreases permeability
  • Increases durability

13
Curing Concrete
  • How concrete is cured
  • Ponding or Immersion
  • Spraying or Fogging
  • Wet Coverings
  • Impervious Paper
  • Plastic Sheets
  • Membrane-Forming Curing Compounds

14
(No Transcript)
15
General Curing Requirements
  • Time 3-7 days
  • Temperature 50-100 F
  • Moisture Saturated at all times

16
Cold Weather Concreting
  • Cold weather exists when, for more than 3
    consecutive days, the following conditions are
    present
  • Average daily temperature is less than 40 F
  • Air temperature is not greater than 50 F for more
    than one-half of any 24-hour period

17
The Main Objectives
  • Prevent concrete from freezing at an early age
    (first 24-48 hours)
  • Assure concrete reaches strength for loading or
    form removal
  • Maintain normal curing conditions
  • Limit rapid temperature changes

18
Concrete Placement Temperatures
  • Dont exceed placing temperature target by more
    than 20 F
  • Higher temp requires more water, increases rate
    of slump loss, and increases thermal cracking

19
Preparation Before Placement
  • Temperature of surfaces in contact with the
    concrete should be above freezing (35 F)
  • Embedments should have temp above 10 F
  • All snow, ice, and frost must be removed
  • Never place on a frozen subgrade. Cover subgrade
    with insulated blankets a few days prior to
    concrete placement.

20
Insulated Curing Box
21
Other Considerations
  • Discuss all aspects of cold weather concreting at
    the pre-construction meeting
  • Watch weather in the spring and fall, must
    provide protection during first 24-48 hours after
    placement

22
Be Prepared!!!
  • Monitor the weather forecast
  • Monitor the temperature of the concrete
  • Have all materials available before placing
    concrete
  • Anticipate the worst case and be prepared for it
  • Schedule the placement during the warmest part of
    the day

23
Remember!!!
  • If you need a coat to be comfortable outside, so
    does the concrete!!!

24
What is Hot Weather Concreting?
  • When concrete is mixed, transported, and place
    under conditions of high ambient temperature, low
    humidity, solar radiation, or wind, an
    understanding of the effects there environmental
    factors have on concrete properties and
    construction operations is required (ACI 305).

25
General
  • Initial curing of concrete test specimens for
    checking adequacy of mix for strength or basis of
    acceptance are cured initially at 60 to 80F
    (16 to 27C), ASTM C31
  • 24hr cure at 100F, 28 day may be 10 to 15
    percent lower than cured ASTM C31
  • drying at early age, strengths will be reduced
    even further

26
Definition of Hot Weather
  • High ambient temperature
  • High concrete temperature
  • Low relative humidity
  • Wind velocity
  • Solar radiation
  • Hot weather is any combination of the above which
    impair quality of fresh or hardened concrete
    and/or cause detrimental results

27
Hot Weather
  • Hot weather concrete problems generally occur
    during the summer season
  • Thermal shrinkage is more severe in the spring
    and fall (temperature differential)
  • When air temperatures are identical, a calm,
    humid day is less severe than a dry, windy, sunny
    day

28
Potential Problems in Hot Weather - Plastic
Concrete
  • Increased water demand
  • Increased rate of slump loss, tendency to add
    water at the jobsite
  • increased rate of setting, resulting in difficult
    handling, finishing, and risk of cold joint
  • Increase for plastic shrinkage
  • Increased difficulty in controlling entrained air
    content.

29
Potential Problems in Hot Weather - Hardened
Concrete
  • Decreased 28 day and later strengths, higher
    water demand, concrete temperatures
  • Increase for drying shrinkage and thermal
    cracking
  • Decreased durability from cracking
  • Increased permeability
  • Increased potential for reinforcing steel
    corrosion due to increased cracking

30
Avoiding Potential Problems
  • Use concrete materials and proportions with
    satisfactory records in hot weather
  • Use cool concrete
  • Use a concrete consistency that permits rapid
    placement and effective consolidation
  • Transport, place, consolidate, and finish with
    least delay
  • Protect concrete against moisture loss at all
    times, during placement and curing period

31
Temp, Slump, Water Demand
32
(No Transcript)
33
Questions?
  • Remember
  • Use Common Sense
  • Temperature effects on your body have very
    similar effects on concrete
  • If you are not sure, ASK!!!
About PowerShow.com